Over the past four decades, blood and marrow transplantation (BMT) has proven to be effective therapy, and even the treatment of choice, for a variety of malignant and nonmalignant diseases that affect the lymphohematopoietic system. Major advances, particularly in the area of supportive care, have decreased the complications of BMT, so that it can be applied to older patients and to severe, but non-fatal, diseases. Newer antibiotic regimens and hematopoietic growth factors have significantly reduced infectious complications. Patient selection, therapeutic monitoring, and less intensive reduced intensity conditioning regimens have substantially decreased regimen-related toxicities such as veno-occlusive disease ofthe liver. Our program has focused on the translation of transplantation biology from the laboratory to the clinic. New preclinical and clinical data already demonstrate that newly developing approaches will improve the outcome of BMT, as well as increase its indications. The foundation of our institution's BMT research has been two ongoing Program Projects that study various aspects of transplantation biology. Our translational clinical studies funded by these grants over the past decade have found that high-dose Cy post BMT effectively modulated alloreactivity (GVHD and graft rejection), allowing safe and effective haploidentical related BMT. However, although our group and others have had great success in piloting novel clinical approaches, it is difficult for a single program to carry out definitive trials that test clinical approaches that appear promising. Thus, a formal clinical network that can rapidly and efficiently conduct multi-center trials in BMT is critically important, especially with the ongoing rapid development of promising new therapies. Accordingly, our results with haploidentical related BMT have been confirmed in a recently completed BMT Clinical Trials Network (CTN) trial (BMT CTN 0603). Not only did the BMT CTN trial demonstrate the effectiveness of this approach, but also that it can be safely exported. Our specific aims as a Core Clinical Center are: 1) participate in multi-center trials through the BMT CTN, and 2) propose a clinical trial for implementation in the Network: a randomized, phase III trial non-myeloablative umbilical cord blood transplantation versus non-myeloablative haploidentical BMT. RELEVANCE (See instructions): Our group and others have had great success in piloting new clinical approaches for BMT patients. However, it is difficult for a single institution to carry out definitive trials that test promising new clinical. Thus, a formal clinical network that can rapidly and efficiently conduct multi-center trials in BMT is critically important.